The present invention relates to a wire bonding inspecting apparatus, and more specifically to a wire bonding inspecting apparatus for automatically inspecting wires bonded between a semiconductor chip and leads.
In order to secure the quality and reliability of a semiconductor device, it is indispensable to inspect wires bonded between a semiconductor chip and leads, to determine whether wires are bonded at incorrect positions; whether wires are extended straight; if wires are not cut off; or the like. When the above-mentioned inspection is performed visually, there exist various problems of lower reliability due to human error, irregularity due to worker error, waste of time because a long time is required from when wires have been bonded to when the inspection is started, etc. Recently, therefore, it is usual to automatically inspect the wire bonding of a semiconductor device by an apparatus.
In the conventional automatic wire bonding inspecting apparatus, in general, an image of a semiconductor chip on which wires have been bonded is optically formed on a screen as a magnified picture; transduced into video signals; and then compared with reference data (criteria) to determine whether the semiconductor chip is acceptable or unacceptable.
In the conventional automatic wire bonding inspection apparatus, however, there exists a problem in that it is impossible to adapt the inspecting apparatus to various semiconductor chips of different sizes. This is because an area at which video signals can be generated is fixedly determined or not adjustable for each inspecting apparatus. In other words, when an inspecting apparatus designed for a relatively large-sized semiconductor chip is used to inspect a relatively small-sized semiconductor chip, there exists a wide wasteful inspection area. In contrast, when an inspecting apparatus designed for a relatively small-sized semiconductor chip is used to inspect a relatively large-sized semiconductor chip, there exists an uninspectable area, because the apparatus cannot cover the chip area perfectly.
In more detail, FIG. 1A is an optically enlarged inspection area in which there are shown a semiconductor chip 101, a number of leads 104 and a number of wires 102 bonded between a pad 103 of the chip 101 and the leads 104. In this example, since the size of the semiconductor chip 101 is relatively small, an inspection area 41 enclosed by dashed lines can cover the wires 102, the pad 103 and the bonded positions 105 on the leads 102 all to be inspected, thus resulting in no specific problems.
In contrast, FIG. 1B is a similar inspection area in which there are shown a relatively large-sized semiconductor chip 201, a number of leads 204, and a number of wires 202 bonded between a pad 203 of the chip 201 and the leads 204. In this example, however, since the size of the semiconductor chip 201 is relatively large and further, the inspection area 41 is fixed constant, the inspection area 41 enclosed by dashed lines cannot cover all the bonded positions 205 on the leads 202, thus resulting in the problem in that it is impossible to inspect all of the wire bonding conditions.
Further, since the resolving power of a video unit (video signal generator) is usually constant over all of the inspection area, when the highest possible resolution is required for a semiconductor chip of predetermined size, the semiconductor chip must be located accurately on an inspection base; that is, there exists another problem in that the allowability of offset of the semiconductor chip to be inspected relative to the inspection base is extremely narrow. In more detail, with reference to FIG. 1C, where an inspectable area 61 enclosed by the dashed line is determined to be a little broader than an inspection area 62 enclosed by solid line in order to increase the resolution, there exists a problem in that an allowable offset dimension x on one side is extremely narrow and therefore the allowability of offset in locating a semiconductor chip on the mounting base is extremely small. Although it is possible to increase the allowability x by increasing the inspection area 61, since the resolution decreases with an increasing inspection area 61, there arise other various problems in that a more expensive video signal generator is required; a longer inspection time is required and, therefore, the inspection speed slows.